Women are dying during pregnancy because they are unaware they have heart problems, experts warned.
Heart disease is the leading cause of maternal death in the UK – but in 77 percent of cases the women were unaware of a heart condition before they became pregnant, according to a study.
Doctors often ignore the warning signs, mistakenly believing heart problems would not strike young women, it said.
Yet pregnant women are at extra risk because of the strain carrying a baby places on the heart and for those with underlying conditions pregnancy can be fatal. The symptoms of cardiovascular disease can be masked by the pregnancy.
Experts said all women should ask relatives about their medical history before having a child, to check whether there is a family history of heart problems.
Maternal death rates linked to heart problems have doubled since the 1980s, the report reveals.
The Confidential Enquiry into Maternal Deaths found that one in four maternal deaths are linked to cardiac disease.
On of the authors, Dr Rachael James, consultant cardiologist at Sussex Cardiac Centre, who will present the findings today at the British Cardiovascular Society conference in Manchester, said: "This inquiry highlights, once again, that we need to see action being taken to stop young women dying from heart disease."
She added: "Women trying for a baby or mothers-to-be should also look at their family history for the possibility of any undiagnosed inherited heart conditions, which are often marked by the sudden or unexplained death of relatives."
But the report also stressed that doctors need to take responsibility.
The authors wrote: "This report highlighted many instances when pregnant and post-partum women [those who have given birth] had clear symptoms and signs of cardiac disease, which were not recognised, often because the diagnosis was simply not considered in a young pregnant woman.
"There was evidence of a focus on excluding, rather than making, a diagnosis in women who presented repeatedly for care."
The actual numbers who die are small – 2.18 women per 100 000 maternities died of cardiac problems during or soon after pregnancy between 2012 and 2014, the report found.
This equates to roughly 17 every year – a quarter of the 67 women who die during pregnancy or in the first six weeks after a baby is born in the UK and Ireland each year.
But cardiac-related pregnancy deaths have more than doubled from 1.01 per 100 000 since 1985.
The authors said they have increased because there are more older mothers, obesity is increasing and pathologists are better at spotting that death has been caused by heart problems.
The report found that the most common heart-related cause of maternal death was sudden cardiac death followed by coronary heart disease.